The neurotransmitter dopamine plays an important role in the brain reward process. Dysfunction of the dopaminergic system is implicated in addictive behaviors. The relationship between dopaminergic system and cocaine addiction has been particularly well characterized. Numerous studies have shown that the D1 dopamine receptor subtype is involved in mediating the effects of cocaine. Acute and chronic administration of cocaine has been reported to alter the expression levels of D1 receptors in the mesocorticolimbic pathway. The molecular mechanisms and extra cellular factors that mediate the changes in dopamine receptor expression in cocaine-treated animals are largely unknown;however some reports have indicated that changes occur at the post transcriptional level. We have recently determined some of the extra cellular factors and molecular mechanisms that regulate the expression of the D1 dopamine receptor gene. Using a catecholaminergic neuronal cell line we determined that the endogenous D1 dopamine receptor is regulated at the post-transcriptional level during in vitro differentiation, and also following brain-derived neurotrophic factor treatment. Our preliminary studies also show that the post-transcriptional regulation of D1 dopamine receptor expression is mediated by cis-acting elements in the 3'untranslated region of the gene. In this R03 project, we test a novel hypothesis that posttranscriptional modulation of D1 dopamine receptor expression by acute and chronic administration of cocaine is mediated by microRNAs that bind cis-acting elements in the 3'untranslated region of the D1 receptor gene. To test this hypothesis, we will use the Drd1a-EGFP reporter transgenic mice generated by the NINDS Gene Expression Nervous System Atlas (GENSAT) project. Following acute and chronic cocaine treatment of Drd1a-EGFP reporter transgenic mice, we will evaluate the expression of D1 receptor mRNA and D1 receptor protein the nucleus accumbens, caudate, cortex, hippocampus and ventral tegmental area. In addition, we will also assay the expression of putative microRNAs that target the D1 receptor gene in the cocaine-treated animals from various brain regions. The goal of this R03 project is to determine if cocaine-induced changes in D1 dopamine receptor expression can be related to changes in expression of a specific microRNA, and to demonstrate, using primary cultures of D1 receptor-expressing neurons, that altering the expression of this microRNA will also alter the expression of D1 receptor protein. To date, there have been no reports of microRNAs regulating dopamine receptor expression. The results from this project would open a new area of research in dopamine receptor biology and improve our understanding of molecular mechanisms that regulate changes in dopamine receptor expression in cocaine addiction in particular, and addictive processes in general. PUBLIC HEALTH RELEVANCE: The goal of this proposal is to determine the role of microRNAs in mediating regulation of D1 dopamine receptor expression in cocaine addiction. The project will identify the microRNA that is involved and demonstrate how it mediates the post-transcriptional regulation of D1 receptor expression in cocaine-treated animals. The results of this proposal will open a new area of research in dopamine receptor biology and lead to the development of potentially novel therapeutic methods for treating cocaine addiction.